Disappointing.
As someone who has read Bernard Cornwell's series and watched all of Last Kingdom, I felt quite underwhelmed by this movie. The Netflix series strayed from the books many times, as is to be expected, but almost always made up for it with excitement and good writing. That was not the case in this film.
Aethelstan is done a great disservice. Not for the arbitrary focus on his homosexuality, but his complete naevity and poor judgement. Remember this was the first King to unite Britain.
So many characters unmentioned. The series went far off of the books by making certain character more important, which I appreciated. Then the movie just decided to forget that.
There are other points that could be named, but I think others have stated them. I recommend reading,The Saxon tales by Bernard Cornwell, the first book of which is, the Last Kingdom. Or indeed any of his other books.